Mobile communications systems, such as cellular or personal communications services (PCS) systems, are made up of a plurality of cells. Each cell provides a radio communication center in which a mobile station establishes a call with another mobile station or a wireless unit connected to a public switched telephone network (PSTN). Each cell includes a radio base station, with each base station connected to a mobile switching center that controls processing of calls between or among mobile stations or mobile stations and wireless terminals.
Various wireless protocols exist for defining communications in a wireless network. One such protocol is the time-division multiple access (TDMA) standard, such as the TIA/EIA-136 standard provided by the Telecommunications Industry Association (TIA). Another TDMA-based wireless communications technology is the Global System for Mobile (GSM) technology. According to TDMA, each radio frequency (RF) carrier carries a frame that is divided into plural (e.g., six or eight) times slots to increase the number of mobile stations that can be supported per RF carrier.
Traditionally, wireless networks have been designed for carrying circuit-switched voice traffic. However, with the explosion of the Internet and intranets, packet-switched communications (e.g., web browsing, electronic mail, and so forth) have become common. As a result, packet-switched wireless technologies are being developed to transition to higher bandwidth and more efficient packet-switched communications of data as well as voice and other forms of real-time data over wireless networks.
Several packet-switched wireless technologies have been proposed to provide more efficient connections between a mobile station and a packet data network, such as an Internet Protocol (IP) network. One such technology is the General Packet Radio Service (GPRS) technology. One version of GPRS is adopted in GSM (Global System for Mobile) Release 1997. To provide further advanced features related to packet-switched communications, a later version of GPRS, referred to as Enhanced GPRS (EGPRS), is part of 3GPP (Third Generation Partnership Project) UMTS (Universal Mobile Telecommunication System) Release 1999 (also referred to as Release 3).
For even higher data rates, later versions of the 3GPP UMTS specification have been adopted. UMTS is based on the wideband code-division multiple access (W-CDMA) technology. In addition, an enhanced version of the Enhanced Data Rate for Global Evolution (EDGE) technology is referred to as the GSM/EDGE Radio Access Network (GERAN) technology.
As the various standards evolve, an issue that is raised is compatibility of radio systems (such as base stations) with legacy equipment, such as legacy mobile stations. Without addressing compatibility issues, newly developed systems may render legacy mobile stations obsolete and unusable. A need thus exists for a method and apparatus to enable radio systems that operate according to newly developed standards to work with legacy mobile stations.